1. Field of the Invention
The present invention relates generally to the fields of antibodies, angiogenesis and tumor treatment. More particularly, it provides human anti-VEGF antibodies that specifically inhibit VEGF binding to only one (VEGFR2) of the two VEGF receptors. Such antibodies are designed to inhibit angiogenesis and induce tumor regression, and yet have improved safety due to their specific blocking properties. The antibody-based compositions and methods of the invention also extend to the use of immunoconjugates and other therapeutic combinations, kits and methods.
2. Description of the Related Art
Tumor cell resistance to chemotherapeutic agents represents a significant problem in clinical oncology. In fact, this is one of the main reasons why many of the most prevalent forms of human cancer still resist effective chemotherapeutic intervention, despite certain advances in this field.
Another tumor treatment strategy is the use of an “immunotoxin”, in which an anti-tumor cell antibody is used to deliver a toxin to the tumor cells. However, in common with chemotherapeutic approaches, immunotoxin therapy also suffers from significant drawbacks when applied to solid tumors. For example, antigen-negative or antigen-deficient cells can survive and repopulate the tumor or lead to further metastases.
A further reason for solid tumor resistance to antibody-based therapies is that the tumor mass is generally impermeable to macromolecular agents such as antibodies and immunotoxins (Burrows et al., 1992; Dvorak et al., 1991a; Baxter and Jain, 1991). Both the physical diffusion distances and the interstitial pressure within the tumor are significant limitations to this type of therapy. Therefore, solid tumors, which make up over 90% of all human cancers, have thus far proven resistant to antibody and immunotoxin treatment.
A more recent strategy has been to target the vasculature of solid tumors. Targeting the blood vessels of the tumors, rather than the tumor cells themselves, has certain advantages in that it is not likely to lead to the development of resistant tumor cells, and that the targeted cells are readily accessible. Moreover, destruction of the blood vessels leads to an amplification of the anti-tumor effect, as many tumor cells rely on a single vessel for their oxygen and nutrients (Burrows and Thorpe, 1993; 1994). Exemplary vascular targeting strategies are described in U.S. Pat. Nos. 5,855,866 and 5,965,132, which particularly describe the targeted delivery of anti-cellular agents and toxins to markers of tumor vasculature.
Another effective version of the vascular targeting approach is to target a coagulation factor to a marker expressed or adsorbed within the tumor vasculature (Huang et al., 1997; U.S. Pat. Nos. 5,877,289, 6,004,555, and 6,093,399). The delivery of coagulants, rather than toxins, to tumor vasculature has the further advantages of reduced immunogenicity and even lower risk of toxic side effects. As disclosed in U.S. Pat. No. 5,877,289, a preferred coagulation factor for use in such tumor-specific “coaguligands” is a truncated version of the human coagulation-inducing protein, Tissue Factor (TF), the major initiator of blood coagulation.
Although the specific delivery of toxins and coagulation factors to tumor blood vessels represents a significant advance in tumor treatment, certain peripheral tumor cells can survive the intratumoral destruction caused by such therapies. Anti-angiogenic strategies would therefore be of use in combination with the tumor destruction methods of U.S. Pat. Nos. 5,855,866 and 6,004,555.
Anti-angiogenic tumor treatment strategies are based upon inhibiting the proliferation of budding vessels, generally at the periphery of a solid tumor. These therapies are particularly effective in reducing the risk of micrometastasis and inhibiting growth of a solid tumor after, or in conjunction with, more conventional intervention (such as surgery or chemotherapy).
Angiogenesis is the development of new vasculature from preexisting blood vessels and/or circulating endothelial stem cells (Asahara et al., 1997; Springer et al., 1998; Folkman and Shing, 1992). Angiogenesis plays a vital role in many physiological processes, such as embryogenesis, wound healing and menstruation. Angiogenesis is also important in certain pathological events. In addition to a role in solid tumor growth and metastasis, other notable conditions with an angiogenic component are arthritis, psoriasis and diabetic retinopathy (Hanahan and Folkman, 1996; Fidler and Ellis, 1994).
Angiogenesis is regulated in normal and malignant tissues by the balance of angiogenic stimuli and angiogenic inhibitors that are produced in the target tissue and at distant sites (Fidler et al., 1998; McNamara et al., 1998). Vascular endothelial growth factor-A (VEGF, also known as vascular permeability factor, VPF) is a primary stimulant of angiogenesis. VEGF is a multifunctional cytokine that is induced by hypoxia and oncogenic mutations and can be produced by a wide variety of tissues (Kerbel et al., 1998; Mazure et al., 1996).
The recognition of VEGF as a primary stimulus of angiogenesis in pathological conditions has led to various attempts to block VEGF activity. Inhibitory anti-VEGF receptor antibodies, soluble receptor constructs, antisense strategies, RNA aptamers against VEGF and low molecular weight VEGF receptor tyrosine kinase (RTK) inhibitors have all been proposed for use in interfering with VEGF signaling (Siemeister et al., 1998). Following the inhibition of tumor growth in mice using a murine antibody, (Kim et al., 1993; Asano et al., 1998; Mesiano et al., 1998; Luo et al., 1998a; 1998b; Borgstrom et al., 1996; 1998), a humanized anti-VEGF antibody termed Avastin (bevacizumab) (Presta et al., 1997) has been approved for clinical use (Hurwitz et al., 2004).
Other murine antibodies that recognize VEGF and inhibit VEGF-induced functions have been reported. These include the murine antibody termed 2C3, which has the advantage of inhibiting VEGF binding to only one of the two primary VEGF receptors (Brekken et al., 2000). By blocking VEGF binding to VEGFR2, but not VEGFR1, the murine 2C3 antibody has an improved safety profile, maintaining beneficial effects mediated via VEGFR1 (Brekken et al., 2000; U.S. Pat. Nos. 6,342,219, 6,524,583, 6,342,221).
The inventors have recognized, however, that the identification of additional agents that recognize VEGF and inhibit VEGF-induced angiogenesis would be of benefit in expanding the number of therapeutic options. For example, the murine 2C3 antibody, although promising, has certain limitations. In particular, the 2C3 antibody does not bind to mouse VEGF, meaning that it cannot be used in preclinical studies using mouse syngeneic tumors. The most effective translation from preclinical studies to clinical use would thus benefit from the development of a new antibody that binds to both mouse and human VEGF.
In addition, the inventors have recognized that the development of therapeutic agents for the treatment of humans that are better tolerated from an immunological perspective would be advantageous. In this regard, human antibodies generally have at least three potential advantages for use in human therapy. First, the human immune system should not recognize the antibody as foreign. Second, the half-life in the human circulation will be similar to naturally occurring human antibodies, allowing smaller and less frequent doses to be given. Third, because the effector portion is human, it will interact better with the other parts of the human immune system, e.g., to destroy target cells more efficiently by complement-dependent cytotoxicity (CDC) or antibody-dependent cellular cytotoxicity (ADCC).
However, although human antibodies are generally recognized to display these advantages, it is known that the development of human antibodies that have high enough affinities and appropriate functional properties to make them candidates for successful human therapy is by no means straightforward. The art therefore still lacks agents that inhibit VEGF-induced angiogenesis for the safe and effective treatment of humans, and poses challenges to the development of such agents.